This invention relates to a compliant adhesive sealant for use in bonding parts, especially metal lids, to chip packages, especially ceramic chip packages. In particular, it relates to a blend of a solution of a cycloaliphatic epoxy and a polyimidesiloxane which has a high siloxane content.
In typical ceramic packages, integrated circuit (IC) chips are attached to the package and are sealed under a metallic lid. In hermetic packages, the lid is welded to a metallization layer, while in non-hermetic packages, an organic adhesive can be used. Organic adhesives are less expensive to use because they bond at lower temperatures than those required for glass-sealing. In order to obtain a reliable bond between materials that have different expansivities (CTEs), a compliant (low modulus) flexible adhesive is required.
Silicone resins are a commonly used adhesive sealant for attaching metallic lids to ceramics. To complete the bond, it is necessary to cure the silicone resin in an oven. Since the silicone resin is a thermoset resin and lacks strength at high temperatures, hydrostatic pressure must be applied to the oven in order to retain integrity of the seal. This bond is a batch process and it constitutes a bottleneck in manufacturing the printed circuit boards.